1. Field of the Invention
This invention relates to movable work-in-process (WIP) transports and more particularly to a WIP transport apparatus for moving materials requiring a temperature and humidity controlled environment.
2. Description of Related Art
Assemblies for carrying items currently exist for transporting materials from one area to another. Examples of such transport units are wheeled platforms with or without motor drives and wheeled shelves. Such units are used to transport a variety of materials including items extremely sensitive to the environment. Items such as disk drives, semiconductor wafers, and flat panel displays require clean environments and controlled temperature and humidity conditions at all times during their manufacture. Environmental control can become a problem in the manufacture of these materials, especially as they are transported between processing tools. During this transport, these materials may be exposed to contaminants such as particles or electrostatic charges as well as temperature and humidity variations. Exposure to uncontrolled environmental conditions can produce, for example, uneven deposition layers in semiconductors, induced thermal stresses, reduced yield, and an overall decrease in the quality of the final product.
To store materials, e.g., semiconductor wafers, in controlled environments between processing stages, specially designed storage containers are used as an intermediate storage. However, these containers are static and not easily transportable, thus requiring additional transport and exposure to the environment to and from these containers. Environment controlled transportation units currently exist to transport sensitive materials, e.g., motion picture films. See U.S. Pat. No. 4,922,721 (Robertson et al.), which is incorporated herein by reference. However, there is a need for a transport unit which controls a variety of environmental factors for transporting sensitive materials such as semiconductor wafers, disk drives, flat panel displays, and other electronic devices.